Historically, the material of choice for insulations employed on pacing/defibrillation leads has been silicone due to its superior handling characteristics as compared to its polyurethane material counterpart. The drawback however, is the compromised abrasion resistance that the silicones exhibit. A breach in the outer insulation employed on leads has been extensively reported in the literature and is an especially potentially serious failure mode of Implantable Cardioverter Defibrillation (ICD) systems. This failure mode can result in the inhibition of the delivery of high voltage therapy due to a direct arc from the lead to the can if the insulation breach exposes one of the defibrillation conductors. The failure mode can also manifest itself in the form the delivery of inappropriate therapy due to the detection of noise if the breach exposes any of the sensing or pacing conductors of the lead.
The problem is further compounded by the increasing number of leads that are implanted in patients and their subsequent interaction resulting in abrasion.
Known techniques, materials, and constructions which preceded the present invention include:                a soft polyurethane composition having a low level of an aromatic phosphate or phosphonate plasticizer that will perform well as a self-sealing liner to flat-proof pneumatic tires, and will withstand the high temperatures of the tire retread process and still be functional;        an implantable lead having a helically wound conductor with a surrounding tubular insulating layer of elastomeric material such as silicone or polyurethane and an additional coaxial tubular exterior biocompatible layer of porous PTFE having a microstructure of nodes interconnected by fibrils, the exterior tubular layer of porous PTFE fitted coaxially over the elastomeric tubular layer whereby the porous PTFE tubular layer is in longitudinal compression and the fibrils within the microstructure have a bent and wavy appearance and such that any portion of the length of the porous PTFE tubing in longitudinal compression allows that portion of the length of the lead wire to be extensible to a controlled extent limited by the straightening of the bent fibrils within the porous PTFE microstructure;        a lead exhibiting improved combined biodegradation, blood surface compatibility, wear and flexibility characteristics including an outer or first insulation of silicone encircling the conductor and a second insulation of polyurethane encircling the silicone rubber insulation;        a continuous sheath of open-celled porous plastic, preferably ePTFE, is used on the outside of an implantable lead, such that when the pores of the sheath are filled with saline, the lead can deliver defibrillation energy through the pores in the plastic, pore size being chosen to discourage tissue ingrowth while allowing for delivery through it of defibrillation energy.        an extractable lead contains a hydrogel coating having a thickness increase greater than 10% when hydrated, the thick coating used to provide a shear layer so that the coating tears during extraction, either at the coating/lead interface, between layers of the coating itself, or at the coating/tissue interface.        
None of the foregoing instances disclose or suggest the present invention and it was in light of the foregoing that the present invention was conceived and has now been reduced to practice.